1. Field of the Invention
The present invention relates to a driving circuit and a driving method for driving an LCD (Liquid Crystal Display) panel.
The present application claims priority of Japanese Patent Application No. 2005-341783 filed on Nov. 28, 2005, which is hereby incorporated by reference.
2. Description of the Related Art
In recent years, as technology of a display device has progressed, a liquid crystal television set using an LCD panel for screen displaying has become commercially practical. FIG. 7 is a diagram showing an example of configurations of a conventional liquid crystal television set using an overdriving operation circuit, as disclosed in prior art Patent Document 1 (Japanese Patent Application Laid-open No. Hei4-365094). In the liquid crystal television set shown in FIG. 7, synchronizing signals extracted through a television (TV) linear circuit 52 from signals received via an image receiving channel and selected by a tuner 51 are output to a synchronizing control circuit 53 and video signals including Y/C (luminance/color) signals are output to an analog to digital (A/D) converting circuit 54. The A/D converting circuit 54 converts input video signals into digital signals.
Video data output from the A/D converting circuit 54 and to be displayed in a current field is compared in a ROM (Read Only Memory) 56 with image data stored in an image memory 55 and obtained one field before and then a signal representing a result from the comparison is output to a segment electrode driving circuit 58. A common electrode driving circuit 57 generates a signal to commonly control each common electrode of a liquid crystal panel 59 in accordance with a synchronizing control signal fed from the synchronizing control circuit 53. In the liquid crystal panel 59, by the above operations, an image is displayed to provide a preset pattern in a manner based on horizontal/vertical synchronizing signals separated by the synchronizing control circuit 53 from signals received through the image receiving channel and in accordance with control signals to commonly control each common electrode fed from the common electrode driving circuit 57 and in a manner driven by using an overdriving voltage based on data in the first frame and by using a voltage of a pixel electrode based on data in the second frame.
According to technology disclosed in prior art Patent Document 1 (Japanese Patent Application Laid-open No. Hei4-365094), it is reported that, by performing overdriving operations to achieve a sharp rise or sharp fall in optical transmittance of an LCD and to improve a response speed of a liquid crystal panel, it is made possible to speedily track an image which changes rapidly.
Also, a liquid crystal display device including a liquid crystal panel having a liquid crystal layer and an electrode to supply a voltage to the liquid crystal layer and a driving circuit to apply a driving voltage to the liquid crystal panel is disclosed in prior art Patent Document 2 (Japanese Patent Application Laid-open No. 2003-172915) in which, when the liquid crystal panel shows an extreme value in a voltage-transmittance characteristic curve at a voltage exceeding a maximum gray level voltage, the driving circuit supplies, in accordance with a combination of an input image signal existed one vertical period before and an input image signal existing during a current vertical period, a driving voltage obtained by overshooting a gray level voltage corresponding to an input image signal occurring during a predetermined current vertical period is applied to the liquid crystal panel and, as a result, a response speed is improved.
Another liquid crystal display device to display an image by using a liquid crystal panel is disclosed in prior art Patent Document 3 (Japanese Patent Application Laid-open No. 2004-287139) in which a first storing means to store a previous image signal occurred one vertical display period before and a second storing means to store a previous image occurred two vertical display periods before, an enhancement converting means to obtain an enhancement converting signal for compensating for changes in optical response characteristics of the liquid crystal display panel from a previous image signal occurred one vertical display period before stored in the first storing means and from an image occurred two previous vertical display periods before stored in the second storing means and an image signal in a current vertical display period are provided and, therefore, when gray-level transition occurs in an input image signal, it is made possible to compensate for changes in optical response characteristics of a liquid crystal display pattern and to make a liquid crystal reach a transmittance (target gray-level luminance) determined by an input image signal without fail after the elapse of one vertical display period, thus enabling a desired gray-level luminance to be displayed all the time and high-quality image display to be achieved.
However, in the conventional driving circuit for the liquid crystal television set shown in FIG. 7, the LCD is driven by performing an overdriving operation using gray level voltages between the minimum gray level voltage and the maximum gray level voltage and, therefore, a wide variety of intermediate shades of gray can be selected, which provides big advantages, however, when a gray level voltage near the maximum gray-level voltage is selected, since a voltage to be used for overdriving is almost equal to a voltage of a pixel electrode, almost no effect can be expected that, by improving a response speed of a liquid crystal panel, an image changing rapidly can be speedily tracked.